The present invention relates to spin coating technology and fluid feeding technology. More particularly, it is effective when utilized for spin coating techniques and liquid feeding techniques in the manufacture of semiconductors, magnetic disks, multilayer wiring circuit boards, chemicals, foods, etc.
The present invention is applied especially to a liquid feeding apparatus which feeds liquids at predetermined rates in highly pure states and under precise speed controls.
In the manufacturing processes of the semiconductor industry, the magnetic disk industry, etc., there are often used chemical processes which employ liquids such as pure water, acids, alkalis, organic solvents and photoresists.
As regards the semiconductor manufacturing processes, the dimension of finishing which is required for production based on the treatment processes employing liquid chemicals has been reduced from 0.8 .mu.m to 0.5 .mu.m, and defective shapes as well as defective characteristics which are ascribable to the mixing of impurities such as air bubbles and foreign matter have occurred frequently. This situation has necessitated a technique which eliminates the impurities in the chemical liquid, such as air bubbles and foreign matter, and then feeds the liquid in a clean state.
Moreover, it is common in these fields to switchingly handle various liquids which differ in physical properties, such as viscosities and specific gravities, thus producing fluctuations of liquid feed characteristics.
Under these circumstances, several liquid feeding apparatus have been proposed as prior-art techniques.
First, as an expedient for avoiding the mixing of air bubbles (gas bubbles) in a feed liquid, a method wherein the bubbles are trapped in the filter of a chemical liquid feed section and are removed by a branch pipe is known from the official gazette of Japanese Patent Application Laid-open No. 211920/1987.
Also, as an expedient for avoiding the mixing of foreign matter in a feed liquid, a method wherein a filter, a pump and a control valve are united to prevent the liquid from staying within a liquid feed system and to remove the foreign matter by means of the filter is known from the official gazette of Japanese Patent Application Laid-open No. 500135/1989.
Also, as an expedient for preventing drippings and feed rate fluctuations which are ascribable to the fluctuations of a suck-back rate within a dropping nozzle, a method wherein the suck-back rate within the dropping nozzle is optically measured and is controlled is known from the official gazette of Japanese Patent Application Laid-open No. 21924/1989.
Further, as an expedient for preventing the fluctuations of a liquid feed rate and a suck-back rate, a method wherein the ON/OFF timings of valves for compressing and decompressing a liquid container and a valve for feeding a liquid are independently controlled is disclosed in the official gazette of Japanese Patent Application Laid-open No. 76327/1988.
Also, as an expedient for feeding at a fixed rate a liquid whose viscosity changes with time, a method wherein a period of time for feeding the liquid is automatically set by a timer with the lapse of time is known from the official gazette of Japanese Patent Application Laid-open No. 221463/1987.
In addition, as an expedient for preventing matter from adhering to a dropping nozzle, a method wherein the dropping nozzle is immersed in a detergent liquid during the cessation of liquid feed, whereby a feed liquid remaining in the dropping nozzle is prevented from drying and solidifying, is known from the official gazette of Japanese Patent Application Laid-open No. 8621/1989.